The present invention relates generally to the fields of diagnostic devices and methods of use thereof. More specifically, the present invention relates to a device for diagnosing rheumatoid arthritis.
There are almost 100 disorders that fall under the umbrella classification of arthritis. The most prevalent are osteoarthritis and rheumatoid arthritis. Osteoarthritis (OA) is a disease of wear and tear commonly affecting the elderly. Rheumatoid arthritis (RA) is a systemic auto-immune disorder causing a symmetric inflammatory polyarthritis. Once the inflammatory process is activated, there can be rapid destruction of joints that can, in some cases, be very aggressive. It has been shown that erosive damage occurs within weeks of the onset of the clinical symptoms. Typically, RA involves the small joints of the hands and feet leading to the clinical signs of joint tenderness and swelling.
Despite its prevalence, arthritis can often be a difficult disease to diagnose. Clinical history and physical examination by a specialised medical practitioner are of key importance in diagnosis. However, any diagnosis based upon the personal skills and experience of the examining physician must of necessity contain an element of subjectivity. Among the more objective tests are X-ray investigation and magnetic resonance imaging of the affected joints and serological and immunological analysis of synovial fluid and blood.
Once a diagnosis is made, assessment of prognostic indicators presents further difficulties. For example, RA has traditionally been thought of as one homogeneous disease, but it has become increasingly obvious that there are many subgroups within the patient population. Specifically, while some patients may have minimal disease for 20-30 years with only minor joint deformities and mild disability, other patients may have the disease for less than 5 years and within this time the disease progresses so rapidly that many joints are destroyed and require replacement. Patients in this latter group often have severe functional disabilities in their activities of daily living.
It is becoming clear that there are certain early prognostic features that can suggest that a patient is more likely to have extensive and progressive disease, at least for RA. One of these features is the immunological haplotype where the class 11 MHC HLA-DR 4 and HLA-DR 1 are associated with RA. Unfortunately, immunogenetic haplotyping is expensive and is not a practical tool for the office. Other factors contributing to a poorer prognosis include female gender, high rheumatoid factor titres, multiple joint involvement and early erosive damage. However, no one feature predicts the severity of disease or the extent of involvement at a specific joint.
Current modes of assessment of arthritis (other than clinical examination) include i) plain radiographs, which do not show the very early damage: ii) magnetic resonance imaging which does show early cartilage and bony destruction, but is neither easily available nor inexpensive; and iii) ultrasound imaging which provides a more subjective assessment but thus far has been confined to research units.
All of the above diagnostic methods, and particularly combinations of these methods, may require the services of a rheumatology specialist, immunologist and skilled technical staff, making diagnosis costly, labour intensive and time consuming. In addition, it may take weeks or months for the clinical symptoms to become distinctive enough to allow diagnosis. Unfortunately, by the time symptoms are sufficiently distinct to allow diagnosis by more objective methods, considerable irreversible damage may already be present in the affected joints.
Clearly, it is critical to determine the severity of the disease early on in the clinical assessment. However, this is complicated by the discordance that is often found between the detection of swelling, tenderness and temperature of a joint with plain radiographic assessment which may not yet show any underlying damage. Although the majority of patients with active synovitis do progress on to early radiographic damage, there is a subset of patients who have active synovitis for several years with no apparent radiographic joint damage.
New methods for the early investigation of arthritis are therefore required and infrared spectroscopy may form the basis for such a method. For example, U.S. Pat. No. 5,038,039 teaches an infrared spectroscopy-based method for detecting the presence of anomalies in biological tissues and cells. However, the tissues and/or cells must be removed from the patient in order to be tested.
Similarly, U.S. Pat. No. 5,473,160 teaches a method for diagnosing arthritic disorders using infrared spectroscopy that involves analyzing synovial fluid taken from a joint for anomalies.
It is apparent that there is a real need for a rapid, non-subjective method for the diagnosis of arthritic disorders that has the additional benefits of being low cost, non-labour intensive and does not require the removal of fluid or tissue samples from the patient, that is, a method of diagnosing arthritis that is non-invasive.
The novel method presented here is based upon the combination of near infrared (NIR) spectroscopy with multivariate classification.
NIR spectroscopy measures the wavelengths of near infrared light that are absorbed by a sample, which produces a characteristic fingerprint of the sample. NIR light is absorbed to promote vibrations within molecules. Typically, only absorption band from Oxe2x80x94H, Nxe2x80x94H and Cxe2x80x94H vibrations are seen. The wavelengths of light which are absorbed depend upon the nature of the vibration (stretching, bending etc.) and the nature of the molecules in the bond. Thus, Oxe2x80x94H stretching and Nxe2x80x94H bending vibrations absorb different wavelengths of light. In addition, NIR light can be absorbed to promote low-lying electronic transitions in the metal ions found in proteins such as haemoglobin, myoglobin and cytochromes. The wavelength of light absorbed by the metal ions is influenced by both the oxidation state and local environment. Thus, oxy- and deoxymyoglobin, oxy- and deoxyhaemoglobin and reduced and oxidised cytochrome aa3 all absorb different wavelengths of near infrared light.
It can be seen that the wavelengths of near infrared light absorbed by tissues will provide direct chemical (compositional) and physiological (oxygenation and oxygen utilisation) information. More importantly, near infrared spectroscopy is sensitive to changes in these parameters. In principle, this should allow NIR spectroscopy to be used as a tool to assess joint physiology. We have therefore applied NIR spectroscopy to the characterisation of rheumatoid synovitis.
According to a first aspect of the invention, there is provided a method of diagnosing an inflammatory or ischaemic condition in a joint comprising:
providing a device having:
an emitter arranged to emit a beam of infrared light;
a collector arranged to collect and analyze reflected light, said collector for producing an infrared spectrum; and
a database containing a plurality of spectra previously collected from joints, said spectra being divided into at least two groups: spectra from joints diagnosed as having the inflammatory or ischaemic condition and spectra from nonafflicted joints;
providing a joint;
positioning the device proximal to the joint such that the emitter contacts the joint;
emitting a beam of near infrared light from the emitter into the joint;
collecting and analyzing reflected light from the beam, thereby producing a patient spectrum;
comparing the patient spectrum to the database spectra; and
assigning the patient spectra to a group, thereby diagnosing the joint.
The inflammatory or ischaemic condition may be rheumatoid arthritis.
The patient spectrum may be a mean spectrum of two or more spectra of the joint.
The patient spectrum may be compared to the database spectra over wavelengths of high accuracy.
The wavelengths of high accuracy may be selected from the group consisting of: wavelengths corresponding to oxyhemoglobin to deoxyhemoglobin ratio; wavelengths corresponding to reduced cytochrome aa3; wavelengths corresponding to oxidized cytochrome aa3; wavelengths corresponding to deoxyhemoglobin; wavelengths corresponding to oxyhemoglobin; wavelengths corresponding to cytochrome aa3; wavelengths corresponding to water; wavelengths corresponding to proteins; wavelengths corresponding to lipids; and combinations thereof.
The emitter may be a fibre optic probe.
The database spectra may be divided into three groups: control, early rheumatoid arthritis and late rheumatoid arthritis.
According to a second aspect of the invention, there is provided a device for diagnosing an inflammatory or ischaemic condition in a joint comprising:
an emitter arranged to emit a beam of infrared light;
a collector for producing an infrared spectrum from reflected infrared light; and
a database containing a plurality of prior spectra previously collected from joints, said spectra being divided into at least two groups: spectra from joints diagnosed as having the inflammatory or ischaemic condition and spectra from nonafflicted joints; and
an analyzer for comparing the spectrum to the prior spectra and assigning the spectrum to a group, thereby diagnosing the joint.
The inflammatory or ischaemic condition may be rheumatoid arthritis.
The collector may produce a spectrum that is a mean spectrum comprised of two or more spectra of the joint.
The analyzer may analyze the spectrum for wavelengths of high accuracy and compares the spectrum to the database spectra over the wavelengths of high accuracy.
The emitter may be a fibre optic probe.
The spectra may be divided into three groups: control, early rheumatoid arthritis and late rheumatoid arthritis.